This invention relates to a liquid crystal display panel, and more particularly to a thin film transistor liquid crystal display having color filters integrated with a thin film transistor array (referred to as color filter on array, abbreviated as COA), its array substrate, and its fabrication method.
With the advancement of technology, video products, particularly digital video or image devices, have become common products in everyday lives. In these digital video or image devices, display devices are important components that allow users to obtain information or to further control the operation of the video or image devices.
The sizes of video or image devices have become thinner and lighter. While traditional cathode ray tube (CRT) displays have certain advantages, they take up considerable space and consume more energy. Using optoelectronics and semiconductor manufacturing technologies, flat panel displays, such as thin film transistor (TFT) liquid crystal displays (LCDs), have become popular display products. TFT LCDs have several advantages over traditional CRT displays, such as lower operation voltage, zero radiation, light weight, and smaller volume. TFT LCDs and other flat panel displays, such as plasma displays and electroluminance displays, recently have become a main topic of display researches, and have been viewed as the mainstream display devices of the twenty-first century.
FIG. 1 shows a conventional TFT LCD panel, which typically has a TFT array substrate 102, an opposite substrate 104, and a liquid crystal layer (not shown), which is positioned between the substrates 102 and 104. On the TFT array substrate 102, there is a TFT array 112, which includes scan lines, data lines, and thin film transistors. Between the substrates 102 and 104, there is a frame sealant 106 that is used to seal the space between the substrates 102 and 104 so that the liquid crystal remains within the sealed space. The sealed space is mainly used to display patterns or colors, and thus is referred to as the display area. The frame sealant 106 has a liquid crystal injection hole 108 to facilitate injection of the liquid crystal.
In addition to the conventional TFT LCD panel described above, there is another kind of technique for manufacturing TFT LCD panels, characterized in that color filters (which are thin films) are fabricated directly on the substrate 102 that has the TFT array 112. An advantage of this technique is that the aperture ratio can be increased. The TFT LCD panels that have color filters integrated on the TFT array substrate can be used in products such as thin and light-weight notebooks having high definition displays, LCD televisions, and high-end LCD monitors.
The conventional TFT LCD panel having color filters integrated with the TFT array substrate can have a number of disadvantages.
In the example of FIG. 1, prior to fabricating the color filters directly on the substrate 104 that has the TFT array 112, it is necessary to fabricate the black matrix (BM) first. Many researches have focused on finding ways to reduce the cost and manufacturing time of TFT LCD panels that use the color-filter-on-array technique. When the black matrix and the color filters are fabricated on different substrates, misalignment of the back matrix and the color filters may reduce the product yield rate.
Light emitted by circuitry on the substrate 102 can be leaked from the border 110 (FIG. 1) of the display area, adversely affecting the display quality of the TFT LCD panel. Light can also be leaked from the liquid crystal injection hole 108.
Each TFT in the TFT array 112, or the conducting lines surrounding the TFT array 112, typically has a repair structure (not shown) that can be used to repair defects in the TFT or defects in the signal lines (line defects). In a conventional design, the repair structure is covered by a thick layer of dielectric. Bursts often occur in the dielectric layer during the repair process, preventing the defective TFT or signal line from being repaired.
Each TFT in the TFT array 112 corresponds to a storage capacitor (Cst) that is formed by an insulation layer sandwiched between two metal layers. The upper metal layer is connected to a pixel electrode so that it can be controlled by the TFT. Because of imperfections in the microlithography process, such as imperfections in the development of photoresist or etching process, portions of the dielectric layer may remain between the metal layer and the pixel electrode due to incomplete exposure or incomplete etching, resulting in poor electric contact between the metal layer and the pixel electrode. Such imperfections prevent the storage capacitor from maintaining a specified charge within a specified time to allow the display pixel to show a specified gray level, thus reducing the performance of the display panel.